The present invention generally relates to dialysis systems. More specifically, the present invention relates to automated peritoneal dialysis systems. The present invention also relates to methods of performing automated peritoneal dialysis and devices for performing same.
Due to disease, insult or other causes, a person's renal system can fail. In renal failure of any cause, there are several physiological derangements. The balance of water, minerals and the excretion of daily metabolic load is no longer possible in renal failure. During renal failure, toxic end products of nitrogen metabolism (urea, creatinine, uric acid, and others) can accumulate in blood and tissues.
Kidney failure and reduced kidney function have been treated with dialysis. Dialysis removes waste, toxins and excess water from the body that would otherwise have been removed by normal functioning kidneys. Dialysis treatment for replacement of kidney functions is critical to many people because the treatment is life saving. One who has failed kidneys could not continue to live without replacing at least the filtration functions of the kidneys.
Hemodialysis and peritoneal dialysis are two types of dialysis therapies commonly used to treat loss of kidney function. Hemodialysis treatment utilizes the patient's blood to remove waste; toxins and excess water from the patient. The patient is connected to a hemodialysis machine and the patient's blood is pumped through the machine. Catheters are inserted into the patient's veins and arteries to connect the blood flow to and from the hemodialysis machine. As blood passes through a dialyzer in the hemodialysis machine, the dialyzer removes the waste, toxins and excess water from the patient's blood and returns the blood back to the patient. A large amount of dialysate, for example about 120 liters, is used to dialyze the blood during a single hemodialysis therapy. The spent dialysate is then discarded. Hemodialysis treatment lasts several hours and is generally performed in a treatment center about three or four times per week.
Peritoneal dialysis utilizes a dialysis solution or “dialysate”, which is infused into a patient's peritoneal cavity through a catheter implanted in the cavity. The dialysate contacts the patient's peritoneal membrane in the peritoneal cavity. Waste, toxins and excess water pass from the patient's bloodstream through the peritoneal membrane and into the dialysate. The transfer of waste, toxins, and water from the bloodstream into the dialysate occurs due to diffusion and osmosis, i.e., an osmotic gradient occurs across the membrane. The spent dialysate drains from the patient's peritoneal cavity and removes the waste, toxins and excess water from the patient. This cycle is repeated.
There are various types of peritoneal dialysis therapies, including continuous ambulatory peritoneal dialysis (“CAPD”), automated peritoneal dialysis and continuous flow peritoneal dialysis. CAPD is a manual dialysis treatment, in which the patient connects an implanted catheter to a drain and allows a spent dialysate fluid to drain from the peritoneal cavity. The patient then connects the catheter to a bag of fresh dialysate and manually infuses fresh dialysate through the catheter and into the patient's peritoneal cavity. The patient disconnects the catheter from the fresh dialysate bag and allows the dialysate to dwell within the cavity to transfer waste, toxins and excess water from the patient's bloodstream to the dialysate solution. After a dwell period, the patient repeats the manual dialysis procedure.
In CAPD the patient performs several drain, fill, and dwell cycles during the day, for example, about four times per day. Each treatment cycle typically takes about an hour. Manual peritoneal dialysis performed by the patient requires a significant amount of time and effort from the patient. This inconvenient procedure leaves ample room for improvement and therapy enhancements to improve patient quality of life.
Automated peritoneal dialysis (“APD”) is similar to CAPD in that the dialysis treatment includes a drain, fill, and dwell cycle. APD machines, however, automatically perform three to four cycles of peritoneal dialysis treatment, typically overnight while the patient sleeps. The APD machines fluidly connect to an implanted catheter. The APD machines also fluidly connect to a source or bag of fresh dialysate and to a fluid drain.
The APD machines pump fresh dialysate from the dialysate source, through the catheter, into the patient's peritoneal cavity and allow the dialysate to dwell within the cavity so that the transfer of waste, toxins and excess water from the patient's bloodstream to the dialysate solution can take place. The APD machines then pump spent dialysate from the peritoneal cavity, though the catheter, to the drain. APD machines are typically computer controlled so that the dialysis treatment occurs automatically when the patient is connected to the dialysis machine, for example, when the patient sleeps. That is, the APD systems automatically and sequentially pump fluid into the peritoneal cavity, allow for a dwell, pump fluid out of the peritoneal cavity and repeat the procedure.
As with the manual process, several drain, fill, and dwell cycles will occur during APD. A “last fill” is typically used at the end of APD, which remains in the peritoneal cavity of the patient when the patient disconnects from the dialysis machine for the day. APD frees the patient from having to manually performing the drain, dwell, and fill steps.
However, continuing needs exist to provide improved APD systems. For example, needs exist to provide simplified APD systems that are easier for patients to use and operate. Further, needs exist to provide lower cost APD systems and APD systems which are less costly to operate. Particularly, needs exist to clinically, economically and ergonomically improve known APD systems.
APD systems need to be improved for home use. One common problem with current home systems is that they are susceptible to electrical shock due to “leakage current”. Current that flows from or between conductors insulated from one another and from earth is called “leakage current”. If any conductor is raised to a potential above earth potential, then some current is bound to flow from that conductor to earth. This is true even of conductors that are well insulated from earth, since there is no such thing as perfect insulation or infinite resistance. The amount of current that flows depends on: (i) the potential, (ii) the capacitate reactance between the conductor and earth and (iii) the resistance between the conductor and earth.
For medical equipment, several different leakage currents are defined according to the paths that the leakage currents take. An “earth leakage current” is the current which normally flows in the earth conductor of a protectively earthed piece of equipment. In medical equipment, impedance to earth from an enclosure is normally much lower through a protective earth conductor than it is through the patient. However, if the protective earth conductor becomes open circuited, the patient could be at risk of electrical shock.
“Patient leakage current” is the leakage current that flows through a patient connected to an applied part or parts. It can either flow from the applied parts via the patient to earth or from an external source of high potential via the patient and the applied parts to earth. Other types of leakage currents include “enclosure leakage current”, and “patient auxiliary current”.
Leakage currents are normally small, however, the amount of current required to produce adverse physiological effects in patients is also small. Accordingly, leakage currents must be limited as much as possible by the design of the equipment and be within safety limits.